Referring FIGS. 1 to 3, description will be made on a conventional national emergency management information system, e.g., a digital mobile communications system for local government (Association of Radio Industries and Businesses (ARIB) standards no.: STD-T79). Further, in the drawings, same components having similar functions are designated by same alphanumeric references and description thereof will be omitted.
The conventional mobile communications system for national or municipal disasters prevention in which one local government serves as a basic unit includes a control station, a base station and a mobile station (see, e.g., Japanese Patent Application Publication No. 2006-100911). Generally, a mobile communications system includes a plurality of base stations, a relay station (relay terminal station), a plurality of mobile stations. However, description will be made on an example of a system having a minimum configuration for simplicity.
FIG. 1 illustrates a schematic configuration of the conventional digital mobile communications system for national or municipal disaster prevention. More specifically, FIG. 1 shows an example of the digital mobile communications system having a minimum configuration, that is, a single base station zone system in which a base station covers operations areas of mobile stations. The reference ‘101’ designates a control station, ‘102’ represents a base station zone, and ‘103-1, 103-2, 103-3, 103-4, 103-5, 103-6, . . . , 103-n’ (n is a natural number) present mobile stations. In the control station 101, 104, 105 and 106-1˜106-m designate a control unit, a radio unit and operations console, respectively. In FIG. 1, the base station includes the control unit 104 and the radio unit 105 whose communications area (service area) is included in the base station zone.
Further, the operations consoles 106-1˜106-m are connected to each other and to the control unit 104, by network circuits, e.g., local telephones connected to public switched telephone network (PSTN), an intranet, a LAN (Local Area Network), a WAN (Wide Area Network) and/or the like. If there are plural base stations, i.e., a plurality of base station zones, respective control units 104 of the plural base stations are connected to the operations consoles 106-1˜106-m. 
FIGS. 2A to 2D show views for explaining communication channels related to communications connection services of the mobile communications system shown in FIG. 1.
As shown in FIG. 1, the mobile communications system is configured to provide communications connection service between a plurality of mobile stations 103-1˜103-4, 103-6, . . . , 103-n and the control station 101, communications connection service between mobile stations direct or via the control station 101, in the base station zone 102, or communications connection service between the mobile station 103-5 outside the base station zone 102 and the mobile station 103-4 inside the base station zone 102.
FIG. 2A shows configurations of a downlink radio carrier (frequency: f1) and an uplink radio carrier (frequency: f2), each having 4 channels, i.e., three communication channels S1˜S3 and a control channel.
For example, if the mobile station 103-4 communicates with the operations console 106-1 of the control station 101 via the control unit 104 and the radio unit 105, the communication channel S2 is set as a communication channel, as shown in FIG. 2C. For example, if the mobile station 103-1 communicates with the mobile station 103-2 via the control unit 104 and the radio unit 105, the communication channel S1 is set as a communication channel, as shown in FIG. 2B.
Further, the mobile station 103-4 may communicate with the mobile station 103-5 located outside the base station zone 102, i.e., the communications area (service area) covered by the base station, without passing through, the base station or the control station 101. In such a case, a radio carrier having frequency f3 is set as a communication channel, as shown in FIG. 2D.
FIG. 3 illustrates a schematic configuration of a digital mobile communications system for national or municipal disaster prevention in accordance with another conventional example. When compared to the mobile communications system shown in FIG. 1, there are additionally provided a relay terminal station and a relay terminal zone. References 103′, 301, 302 and 303-1˜303-k (k is a natural number) designate a fixed station, a relay terminal station, a relay terminal zone, and mobile stations in the relay terminal zone 302, respectively. Hereinafter, a mobile station 103 refers to the mobile stations 103-1, 103-2, 103-3, . . . , 103-n and a operations console 106 refers to the operations consoles 106-1˜106-m. 
The radio terminal station 301 temporarily or constantly covers a dead zone, i.e., an area outside the base station zone 102 in a service area of the base station radio relay to provide communications services. Further, the relay terminal station includes an inter-base station relay terminal station for relaying between a base station communications carrier and another base station communications carrier, and a direct communications relay terminal station for relaying between a base station communications carrier and an inter-mobile station direct communications carrier. The relay terminal station 301 shown in FIG. 3 serves as the direct communications relay terminal station.
In FIG. 3, the mobile station 103, the fixed station 103′ and the relay terminal station 301 send data to the radio unit 105 of the base station via an uplink radio carrier (frequency: f2) and the radio unit 105 of the base station send data to the mobile station 103, the fixed station 103′ or the relay terminal station 301 by using a downlink radio carrier (frequency: f1). In the relay terminal zone 302, the mobile stations 303-1˜303-k send data to and receive data from each other via the relay terminal station by using a radio carrier (frequency: f3).
In the case of the mobile communications system shown in FIG. 1, the mobile stations 303-1˜303-k located outside the base station zone 102 cannot communicate with the control station 101 or the mobile station 103 or fixed station 103′ inside the base station zone 102 via the base station. However, in the mobile communications system in which the relay terminal station 301 is provided as shown in FIG. 3, the mobile stations 303-1˜303-k in the relay terminal zone 302 can communicate with the mobile station 103 or the fixed station 103′ in the base station zone 102 via the relay terminal station 301 and the base station.
In the above-described conventional examples, the mobile station in the base station zone sends a ┌position registration request┘ signal to the control station at a constant time period upon and after starting to operate. At this point, if the mobile station is allowed to use in the mobile communications system, i.e., the mobile station has been already registered or newly registration is completed, a ┌position registration acknowledgement┘ signal is returned and, accordingly, the mobile station, becomes able to make a call.
Further, the control station can identify a base station zone to which the mobile station belongs by such position registration thereof and then, upon making a call to the mobile station, send a call signal via the identified base station. As the above, the control station reduces radio traffics between a circuit control unit and a base station, and a base station and a mobile station, by identifying a base station zone to which the mobile station belongs.
However, mobile stations outside the base station zone (an area outside a communications area of the base station, i.e., a dead zone) or in a direct communications state cannot perform a position registration and, therefore, the control station cannot identify these mobile stations. Further, in the mobile communications system in which a relay terminal station is provided, mobile stations located in the relay terminal zone do not perform a position registration because it operates by using a direct communication protocol.
That is, in the mobile communications system including a plurality of base stations and a relay terminal station, it is impossible to identify which base station zone the mobile station in the radio terminal zone belongs to. For that reason, if a call is made to a mobile station located in the radio terminal zone, the control station cannot decide which base station a call signal is sent through. In order to solve this problem, a mobile communications system may send a call signal through all the base station, which can eliminates need for position registration.
In such case, however, there occur problems, e.g., traffic increase between the control station (circuit control) and the base station, and/or unnecessary use of the radio circuit. Further, there also occurs a problem that the control station (operations manager) cannot manage conditions of the mobile station (power on/off, which base station the mobile station belongs to)